The present invention relates to a press die apparatus, which includes a pair of dies for pressing a metal plate and is used to form, for example, separators for fuel cells.
As a separator for fuel cells (hereinafter, referred to as a separator), the one illustrated in FIG. 8 has been known (for example, refer to Japanese Laid-Open Patent Publication No. 2014-213343).
As shown in FIG. 8, a separator is constituted by a metal plate 60, which is made of, for example, titanium and has a thickness of several tens to a hundred and several tens of micrometers. The metal plate 60 has first grooves 61 on the top surface at a predetermined interval. The metal plate 60 also has second grooves 62 on the bottom surface at the predetermined interval. Each second groove 62 is arranged between adjacent two of the first grooves 61. The grooves 61, 62 of the metal plate 60 respectively constitute gas passages for fuel gas (for example, hydrogen) and gas passages for oxidation gas (for example, air).
When forming such a separator, a press die apparatus as shown in FIG. 9 is used conventionally, for example. The press die apparatus includes a die block 70 and a punch 80. The die block 70 has a corrugated first shaping face 71 on the top surface. The punch 80 has a corrugated second shaping face 81 on the bottom, which corresponds to the first shaping face 71 of the die block 70. The punch 80 is selectively brought closer to and separated from the die block 70. With a metal plate 60 placed on the first shaping face 71 of the die block 70, the punch 80 is moved toward the die block 70. Accordingly, the metal plate 60 is pressed between the die block 70 and the punch 80, so that the first grooves 61 and the second grooves 62 are formed on the metal plate 60.
Conventionally, in a pressing operation performed with the press die apparatus, machining oil is applied to the shaping faces 71, 81 of the die block 70 and the punch 80 to reduce friction between contacting surfaces of the die block 70 and the punch 80 and the metal plate 60, thereby protecting the die block 70, the punch 80, and the metal plate 60 from cracking, scratches, and galling.
When pressing a thin metal plate such as a separator, the following drawbacks are caused. That is, when the machining oil between the metal plate 60 and the shaping faces 71, 81 of the die block 70 and the punch 80 is pressurized by the pressure of the pressing operation, the fluid pressure of the machining oil may be locally increased. In such a case, the metal plate 60 may have defects in shaping. For example, the metal plate 60 may be ripped or have spring back.